Always start with transplants. You can buy these from garden centers or sow seed yourself in cell-packs. For a spring crop, set out transplants 4 weeks before the last frost. For fall and winter harvests in the Upper, Middle, and Lower South (USDA 6-8), set them out 10 to 14 weeks before the first fall frost; in Florida and the Coastal South, plant in October. Space transplants 11⁄2–2 ft. apart in rows about 21⁄2 ft. apart.
Feed at planting time with a water-soluble 20-20-20 fertilizer. Water regularly to keep soil evenly moist. Three to 4 weeks after planting, sprinkle 1⁄2 cup of 10-10-10 fertilizer per 10 ft. of row around plants; repeat 3 to 4 weeks later.
Pruning and Harvesting
Sprouts develop progressively from the bottom of the plant toward the top, appearing first as tiny buds within the leaf axils. Removing the terminal growth tip when the plants are 15–20 in. tall makes the sprouts grow larger and mature more quickly; this is a particularly useful technique for spring crops. Harvest sprouts when they’re 1–11⁄2 in. wide.
To prevent a buildup of soil-borne pests, plant Brussels sprouts in a different site each year. Club root is a serious fungal pest in acid soils; apply lime, if necessary, to raise the pH to at least 6.5. Control insects such as cabbage loopers, cabbageworms, cutworms, and root maggots by using floating row covers or ringing the base of the plant with a cardboard collar. Bacillus thuringiensis (Bt) and spinosad also control cabbageworms and loopers.